System for controlling a turbine

ABSTRACT

A system for controlling a turbine is disclosed. The system includes a turbine control fuel governor that has a plurality of VCPIDs operating in parallel with one another. Each VCPID is associated with a respective turbine parameter and one or more external parameters. Each VCPID incorporates feedback from the parallel operating VCPIDs to feed an integral term of a current VCPID in the following manner: a previous derivative gain and a previous proportional gain are summed and subtracted from a selected output for the turbine to yield a result, and the result is input to an integral gain portion of the current VCPID.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. provisionalapplication No. 63/056,951, filed Jul. 27, 2020, and U.S. provisionalapplication No. 63/083,378, filed Sep. 25, 2020, the contents of whichare herein incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to turbines and, more particularly, to asystem and method of controlling a turbine for hydraulic fracturingusing an Adaptive Turbine Digital Engine Control (“ATDEC”) that can beconfigured to adapt to varying inputs external to the turbine andutilize these to govern fuel. With current technology, the turbineengine control is limited to control fuel based on turbine componentsand sensors. The fuel governor is not able, or adaptive, enough tocontrol fuel that is influenced by external stimulus. The intent of thisinvention is to have all critical components on the frac pump directlyinfluence the fuel governor and therefore control the fuel. In addition,the external sensors, like well pressure, will also govern fuel demandof the turbine. From a very high level, the ATDEC will analyze allinputs that govern fuel and choose the one that demands the least amountof fuel (i.e., “Min Select” 9).

In fracking a well, the pressure of the water going down hole must belimited to ensure that the well casing is not ruptured. In existingsystems, the operator of the pumps notices that the pressure is risingat the well head and reduces the pumping rate, barrels per minute. Thisis a manual process that is sometimes implemented too late, or tooearly, or to the wrong degree. Current systems have only a hard shutdownif the pressure is exceeded, if this occurs it slows the operation at aminimum and if all the pumps trip at the same time, the entire wellmight become compromised by “sanding out”.

For additional background: fracking, hydraulic fracturing, is theprocess for improving the performance of oil and natural gas wells. Ituses high pressure fluids to make fissures in rock (usually shale) toallow more mined fluid to flow more freely. In the course of performingthis well completion operation, a high horsepower pump in operated.Starting said pump is often preformed when the well pressure issubstantially high, often 60% or higher than the operating pressureranging from 4 to 9 thousand psi in the Permian Basin. The fluids usedoften include expensive and can cause ground water contamination ifdeposited in the water table. A breakage of the well casing within therange of the water table is unacceptable. To prevent this expensiveproblem from arising, the well is assigned a pressure rating and saidpressure is to be avoided. In state-of-the-art operation of today, ahuman operator is often limiting the rate that the fluid is introducedinto the well. For a fixed flow rate, the pressure of the well willusually rise as more and more fluid is pushed in. The operator noticingthis rise will reduce the rate that the fluid is pushed into the wellhead. Usually this is a slow operation occurring over the course of afew minutes and is readily handled by an attentive operator.Occasionally, this pressure rise can occur within a handful of seconds.Other systems simply hold throttle but do not continually compensate forincreasing pressure. This requires human intervention to reduce thethrottle in order to compensate for the increasing pressure.

FIG. 1 illustrates an exemplary conventional fuel governor for a gasturbine engine used on the Chinook helicopter. This control scheme isbased on the computation of a parameter referred to as NDOT (*). (NDOTis directly proportional to the fuel command which controls fuel flow).This closed loop fuel governor operates as a single NDOT fuel governor 1and time filter to manage multiple input setpoints. This governorcontrols the operation of the turbine to the given set points via a fuelcontrol valve (FCV) command (CMD). For this type of control, a classicPID loop is employed, which is also the main limitation of thesesystems. By utilizing one PID loop, controlling the turbine fuel by anexternal parameter is not as accurate and leads to less efficientoperations. This governor 1 needs to calculate the amount of fuel neededto ensure none of the operational setpoints are exceeded. This type ofcontrol is most accurate when controlling the setpoint (abbreviated as“Set” in the drawings) that is more physically connected to thecombustion of fuel as that is what the FCV command controls. For theT55, N1 refers to the core engine speed and therefore fuel efficiency isthe highest when N1 is the controlling setpoint (the setpoint selectedby Min Select). The same principle applies to a second turbine sensor N2and the turbine temperature EGT but given that there is only on PIDutilized, the efficiency is less when these setpoints are selected byMin Select. This control theory is not accurate enough to controlsetpoints that are detached from the engine and indirectly affected bythe gas turbine

As can be seen, there is a need for an improved digital engine controlthe provides an automated system that is quicker to respond and veryvigilant.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a system for controlling aturbine comprises: a turbine control fuel governor comprising aplurality of VCPID control loops operating in parallel with one another,each VCPID control loop being associated with a respective turbineparameter and one or more external parameters, wherein each VCPIDcontrol loop incorporates feedback from the parallel operating VCPIDcontrol loops to feed an integral term of a current VCPID in thefollowing manner: a previous derivative gain and a previous proportionalgain are summed and subtracted from a selected output for the turbine toyield a result, and the result is input to an integral gain portion ofthe current VCPID.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are included to illustrate certain aspects of thepresent disclosure and should not be viewed as exclusive embodiments.The subject matter disclosed is capable of considerable modifications,alterations, combinations, and equivalents in form and function, withoutdeparting from the scope of this disclosure.

FIG. 1 is a schematic view of a conventional system that runs with asingle governor 1;

FIG. 2 is a mathematical schematic view of an embodiment of the presentinvention, depicting how a governor of the present invention introducesa feedback for the integral term 2 and an input In CNTRL 3 used to turnthe modification on and off based on if it is the controllingproportional-integrative-derivative (PID) control loop. Thismodification is called the Variable Coefficient Proportional IntegrativeDerivative (“VCPID”) (also synonymous with VCPID control loop) as theVCPID utilizes a variable coefficient based on feedback from parallelVCPIDs;

FIG. 3 is a schematic view of a modified conventional control 1implemented with the upgraded VCPID 4, similar to FIG. 1, but with theSEL Out and In CNTRL modifications, upgrading it to use of threeindependent governors, in accordance with the present invention, asopposed to a single governor 1; and

FIG. 4 is a schematic view of the embodiment of the present invention,depicting the addition of an external control/sensor 8 operating withthe parallel independent governors. Min Select 9 serves two functions,it selected the minimum fuel demand from the VCPID and feeds this back10 along with an indication of which VCPID is in control 9.

DETAILED DESCRIPTION OF THE INVENTION

The subject disclosure is described with reference to the drawings,wherein like reference numerals are used to refer to like elementsthroughout. In the following description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the present disclosure such that one skilled in the artwill be enabled to make and use the present invention. It may beevident, however, that the present disclosure may be practiced withoutsome of these specific details.

Broadly, one embodiment of the present invention is at least one turbineengine controller implementing a hybrid fuel governor to control theamount of fuel delivered to a turbine every frame. A frame of time isusually between 5 ms and 20 ms where the controller predicts the amountof fuel needed to consume to maintain operating conditions. Typically,turbine engine controllers implement a closed loop PID controller thatmonitors turbine parameters and utilizes the PID mathematical formula tocalculate the needed fuel per frame but uses only one PID as a fuelgovernor. The present invention will utilize a series of VCPIDs 4 toenable the ATDEC to monitor systems not directly connected to theturbine and control their setpoints by controlling the output power ofthe turbine to these external set points.

In general, and in accordance with the present invention, a VCPID 4 addstwo new feedback inputs to a standard PID calculation: SEL_(output) 2and In CNTRL 3, that allows multiple VCPIDs 4 to work together, or inparallel. FIG. 4 depicts the two feedback mechanisms 9 and 10 that drivethe modified PID loop FIG. 2 inputs 2 and 3. In CNTRL 3 switches thestandard PID loop between modified operation and standard operation.When TRUE 3, the PID calculations in FIG. 2 default to normaloperations. When FALSE 3, the PID calculations utilize the last OUTPUTfrom Min Select 9 and feed that value 10 through the calculationsdefined in 2. This moves the integral portion of the PID loop to thelast output from the in control VCPID 4 and calculates the fuel demandfor the next frame. This feedback allows for a smooth handover betweenVCPIDs, of which one is in control 3.

To take advantage of the ATDEC invention, adding an external VCPID, likewell pressure 8, enables the ATDEC to monitor the well pressure andautomatically adjusts turbine output based on a purely external stimulusallowing for a quicker response. Being an automated system to performthe rate reducing ensures the safety of the well casing, even if theoperator is distracted. This fast automatic response allows running ahigher rate and higher pressures closer to the limits since any suddenincrease in pressure can be detected and mitigation actions taken withinmilliseconds, instead of the operator response time of a few seconds.

The present invention allows for a turbine control that can take overtasks typically done by operators or other control systems, providingfor faster response times, smoother operations, higher reliability, andfiner control than a human operator. Human operators have limitedresponse times and can become distracted when working a highlyrepetitive operations for hours on end. An automated system ties to theheart of the turbine control system is more reliable at tediousoperations, and quicker to respond.

Certain embodiments of the present invention may include an ATDECconfigured as depicted in FIG. 3 that will operate more efficiently thanan older system as depicted in FIG. 1.

Certain embodiments of the present invention may include an ATDECconfigured as depicted in FIG. 4 that will operate more efficiently thanan older system as depicted in FIG. 1 and protect the external well.

Certain embodiments of the present invention may include an ATDECconfigured as depicted in FIG. 4 but with the addition of VCPIDs 4 thatmonitor pump sensors (oil temp, torque) and transmission sensors (oiltemp, torque) to provide a fully integrated ATDEC.

Certain embodiments of the present invention include a fracking pumpcontrol system such that the operator inputs both the rate and thepressure limits and the control system limits the power applied by thepump to stay within those limits and any other pre-programmed limits asindicated by expanded VCPIDs.

In general, a closed loop pump controller first receives a pressuresetpoint from a user (via an input device, such as a graphical userinterface). This is shown, for example, in FIG. 4, which illustrates aWell PSI CMD, which is set via user input. Next, the ATDEC is connectedto a hardware input (e.g., WELL PSI in FIG. 4) to read an analog signal.Third, the pump controller translates the user setpoint to analog scale.Once setup, adjustments are made in the fuel governor at the same ratethe governor is governing turbine speed and temperature. By executing atthe fuel governor level, the most efficient operation of the engine canbe achieved. This is depicted in FIG. 4, where the Well Pressure VCPIDis running in parallel to the N1, N2, and EGT VCPIDs. All of theparallel VCPIDs are connected to two feedbacks from the output of thesystem. Min Select 9 sets the state of whether a VCPID was the lowestdemand for fuel the last time the control loop executed. SEL Out 10 isconnected to the input SEL Output 2 which will be used to calculate thenew fuel command for all VCPIDs that were not in control 3.

Before or during operation, the user inputs the rate and pressurelimits, which are generally a few percentage points below the allowablelimits. The well head pressure transducer is constantly monitored by thecontrol software for, if and when the pressure approaches and/or exceedssaid pressure limit, reducing the pumping rate.

FIG. 2 depicts, mathematically, how the governor (referred to herein asa VCPID) of the present invention is different so that an ATDEC with afuel governor controlling fuel based on an external hardware analoginput 8 (as mentioned above) is possible. As discussed in theBackground, the governor 1 in FIG. 1 contains a classical PID loop, butthis type of loop does not allow for multiple PID calculations inparallel. In comparison, the adapted PID loop in FIG. 2 defines themodifications to a PID loop that incorporates information from the PIDloop in control. This adapted PID loop is referred to herein as a VCPID4.

The VCPID contains two feedback points so that an external VCPID caninitialize it to a current state. The first feedback point isSEL_(output) 2, which is the output of an external VCPID that iscurrently in control of the fuel for the last time frame. SEL_(output) 2uses an external VCPID integral term as current input when another VCPIDis being used. The integral term in the VCPID will utilize the current‘in charge’ VCPID leading to a seamless switch between VCPIDs. In doingso, independent governors can be tuned to very accurate performances ontheir own create a more efficient system. The second feedback point is“In CNTRL” 3, which indicates if this VCPID is currently in control ornot (i.e., whether the VCPID is controlling or utilizing an externalstate).

In this modification to the standard PID, if this PID is NOT in control,it will initialize the integral portion of the calculation with theoutput of an external PID running in parallel and subtracts the previousinternal derivative and proportional terms. The VCPID 4 has thefollowing inputs: In CNTRL 3, CMD Set Point (which is the value thisgovernor 4 should control to), and CUR Value (which is the current valuethat should be driven to the set point).

FIG. 3 illustrates standard turbine setup with no external sensor, butwith the ability to incorporate it, since there are now threeindependent governors (VCPIDs 5, 6, 7) as opposed to FIG. 1, with onlyone governor 1. Accordingly, FIG. 3 is similar to FIG. 1, the originalcontrol, but updated to use the new VCPID 4. The new implementation ofthe simple turbine control implements, for example, three VCPIDs 4 boundto the same variables as that of FIG. 1. An N1 VCPID 5 controls fuelagainst N1 set points and N1 speed, an N2 VCPID 6 controls fuel againstN2 set points and N2 speed, and an EGT VCPID 7 controls fuel againstturbine exhaust temperature set points. This modified application of theVCPID 4 is more fuel efficient, given that the fuel can be tuned to eachparameter independently.

FIG. 4 shows the addition of an external sensor working with parallelVCPIDS. The new VCPID allows for external control of fuel by sourcesthat can be affected by external factors (i.e., an external parameter)other than just the turbine. By having independent VCPIDs, the turbinecan be integrated into complex systems that have external forcesaffecting them. A Well Pressure VCPID 8 implements a VCPID, as describedabove, against well pressure that is affected by other pumps in thesystem. Without explicit coordination, each direct drive turbine pumputilizing the teachings of this disclosure will monitor the effects ofthe other pumps on well pressure and predict fuel based on thatobservation. In this example, a well pressure on a frac site can controlthe fuel and be tuned even though the well pressure is a product of rockformations, other pumps, and other factors. Those with skill in the artwill appreciate that the VCPID can also be applied to other systemcritical sensors like torque and oil temperature. This will create atruly ‘smart turbine control’ that does not simply look at turbineoperational parameters, but instead all operational parameters in anintegrated system.

To make various embodiments of the present invention, these algorithmicsoftware embodiments utilize industrial standard components such aspressure transducers and digital engine controllers, which reduces thecomplexity of implementing the present invention. At least one of eachhead pressure transducer, an engine controller connected to a frackingpump are required. Multiple pressure transducers could also be placed atvarious points in the frack pluming (often referred to as “the iron”)which would serve to not only protect the well head, but also the pump,the missile, it's valves and other elements of the iron.

In use, most commonly, the operator would enter the rate and pressurelimits into the system. The pressure limit will usually be set to thewell casing pressure, but other limiting factors in the iron maybeconsidered and input into this limit. The operator will start up thepumps and command the rate as needed for the frack job. As the frackingoperation continues, commonly, the pressure will rise. If and when thepressure gets to the inputted limit, the engine will begin to limit itspower to prevent the pressure form rising above the pressure limit.Additional uses include water transfer (e.g., fluid pumps) and otherpipeline systems that require monitoring/managing pressure, temperature,and other parameters for safety.

Therefore, the disclosed systems and methods are well adapted to attainthe ends and advantages mentioned as well as those that are inherenttherein. The particular embodiments disclosed above are illustrativeonly, as the teachings of the present disclosure may be modified andpracticed in different but equivalent manners apparent to those skilledin the art having the benefit of the teachings herein. Furthermore, nolimitations are intended to the details of construction or design hereinshown, other than as described in the claims below. It is thereforeevident that the particular illustrative embodiments disclosed above maybe altered, combined, or modified and all such variations are consideredwithin the scope of the present disclosure. The systems and methodsillustratively disclosed herein may suitably be practiced in the absenceof any element that is not specifically disclosed herein and/or anyoptional element disclosed herein.

While apparatuses and methods are described in terms of “comprising,”“containing,” or “including” various components or steps, theapparatuses and methods can also “consist essentially of” or “consistof” the various components and steps. All numbers and ranges disclosedabove may vary by some amount. Whenever a numerical range with a lowerlimit and an upper limit is disclosed, any number and any included rangefalling within the range is specifically disclosed. In particular, everyrange of values (of the form, “from about a to about b,” or,equivalently, “from approximately a to b,” or, equivalently, “fromapproximately a-b”) disclosed herein is to be understood to set forthevery number and range encompassed within the broader range of values.Also, the terms in the claims have their plain, ordinary meaning unlessotherwise explicitly and clearly defined by the patentee. Moreover, theindefinite articles “a” or “an,” as used in the claims, are definedherein to mean one or more than one of the elements that it introduces.If there is any conflict in the usages of a word or term in thisspecification and one or more patent or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

As used herein, the phrase “at least one of” preceding a series ofitems, with the terms “and” or “or” to separate any of the items,modifies the list as a whole, rather than each member of the list (i.e.,each item). The phrase “at least one of” allows a meaning that includesat least one of any one of the items, and/or at least one of anycombination of the items, and/or at least one of each of the items. Byway of example, the phrases “at least one of A, B, and C” or “at leastone of A, B, or C” each refer to only A, only B, or only C; anycombination of A, B, and C; and/or at least one of each of A, B, and C.

What is claimed is:
 1. A system for controlling a turbine, comprising: aclosed loop turbine control fuel governor comprising a plurality ofVCPID control loops operating in parallel with one another, each VCPIDcontrol loop being associated with a respective turbine parameter andone or more external parameters, wherein each VCPID control loopincorporates feedback from the parallel operating VCPID control loops tofeed an integral term of a current VCPID control loop in the followingmanner: a previous derivative gain and a previous proportional gain aresummed and subtracted from a selected output for the turbine to yield aresult, and the result is input to an integral gain portion of thecurrent VCPID control loop.
 2. The system of claim 1, wherein each VCPIDcontrol loop includes a VCPID output that is fed to a minimum selectfunction.
 3. The system of claim 2, wherein the minimum select functionselects a fuel command based on the VCPID outputs, the fuel commandbeing a command that requires the least amount of fuel to not exceed asetpoint to the parallel VCPID control loops.
 4. The system of claim 1,wherein one VCPID control loop is connected to the core engine speed N1.5. The system of claim 1, wherein one VCPID control loop is connected tothe power turbine speed N2.
 6. The system of claim 1, wherein one ormore VCPID control loops are connected to turbine temperatures.
 7. Thesystem of claim 1, wherein one VCPID control loop is connected to wellpressure.
 8. The system of claim 1, wherein one or more VCPID controlloops are connected to torque sensors.
 9. The system of claim 1, whereinone VCPID control loop is connected to turbine oil temperature.
 10. Thesystem of claim 1, wherein one VCPID control loop of the plurality ofVCPID control loops are associated with a pump oil temperature of thepump.
 11. The system of claim 1, wherein one VCPID control loop of theplurality of VCPID control loops is associated with torque at the pump.